Fabrication of semiconductor devices typically involves the deposition and etching of multiple thin film layers on a substrate. This deposition and etching of the film layers is usually done in a vacuum chamber. Controlling the deposition and etch rate uniformity are critically important to the manufacture of the devices. In this regard, precise measurement of the temperature during fabrication is particularly important.
A variety of methods and devices have been developed for this type of temperature measurement. One common approach has been to locate thermocouples, thermistors or resistance thermometers in the chamber to measure the temperature. In some cases, the temperature measuring device has been embedded in the substrate support, where it is protected from the environment of the vacuum chamber. The devices are normally connected by electrical wires to allow the temperature to be read.
Unfortunately, the use of electrical connections with these temperature measurement devices has caused a wide variety of problems. The wires attached to these devices can be undesirable as the metal in the wires may affect the chamber""s magnetic and/or electrical fields. The electrical signals are not desirable when the application requires electrical isolation and/or low electrical noise. The location and/or movement of the item to be measured may make using these temperature measurement devices difficult or impossible. Elements of these devices (e.g. wires, thermocouple junctions) can be damaged by the corrosive chemical environment of the chamber. Such damage can cause erroneous and erratic temperature readings. The attachment of these measuring devices to the chamber can sometimes actually alter the temperatures to be measured. The use of these devices can be impractical when temperature measurements need to be taken over a large area or when many measurements have to be taken in a small area.
One specific problem is that contact between a conventional temperature probe (e.g. a thermocouple) and the substrate can cause defects to be formed on the substrate, around the contact point. These defects can greatly reduce the production yield, increasing both production costs and time.
Another problem is contamination of the substrate and the chamber caused by conventional temperature probes. The high temperature and low pressure environment of the chamber can cause conventional probes positioned in the chamber to out-gas or otherwise discharge contaminates. Adhesives are one type of material known for causing contamination. Mobile ions from the adhesives can contaminate the chamber. Such contamination can easily cause defects on the substrate, lowering the overall production yield. Also, since the contaminates attach to the chamber, cleaning may be required more often, increasing the cost and lowering the production rate.
One approach to these problems has been to employ radiation pyrometry techniques. These techniques measure the temperature of an object by means of the quantity and character of the energy it radiates. In this way a temperature measurement can be made optically from a distance without the use of wires. On example of such an approach is to apply a temperature sensitive material onto the item to be measured, use a light probe to excite the material, causing. it to emit radiation, and then analyzing the emitted radiation to obtain a temperature value.
U.S. Pat. No. 4,560,286, entitled xe2x80x9cOPTICAL TEMPERATURE MEASUREMENT TECHNIQUES UTILIZING PHOSPHORSxe2x80x9d, by Wickersheim, hereby incorporated by reference in its entirety, describes a method and an apparatus for measuring the temperature of an object provided with a phosphor material. One known application of this method and apparatus involves placing a small amount of a temperature sensitive material on the backside of the substrate. A light detecting member is provided within the substrate support member to measure the emitted radiation from the temperature sensitive material. A processor quantifies the emitted radiation and determines the temperature of the substrate.
This approach has several disadvantages. The phosphor material may migrate into the silicon substrate. The process of applying the temperature sensitive material to the backside of the substrate requires additional processing steps, which are both time consuming and expensive.
Another approach is set forth in U.S. Pat. No. 5,876,119, entitled xe2x80x9cIN-SITU SUBSTRATE TEMPERATURE MEASUREMENT SCHEME IN PLASMA REACTORxe2x80x9d, by Ishikawa, et. al., hereby incorporated by reference in its entirety, which discloses a method and apparatus for non-contact temperature measurement of a substrate in-situ. This is achieved by measuring the temperature of a substrate support member and an intermediate member, located between the substrate and the substrate support member. With the intermediate member having a known thermal relationship with the substrate, the temperature of the substrate can be determined by calibration or application of a heat transfer equation. Some embodiments of this apparatus can use an adhesive to secure the intermediate member in place.
Therefore, a need exists for a device that allows for temperature measurement without the use of thermocouples, thermistors or resistance thermometers, or any wires attached thereto. The device needs to be capable of measuring the temperature remotely, without needing to be in direct contact with the item being measured (e.g. the substrate should not be directly contacted). The device must not cause contamination of other structures, such as the substrate or the chamber, by out-gassing or any other discharge. The device and its use should minimize the overall cost and the production time, and maximize the production yield.
Some embodiments of the present invention include a sensor having a temperature sensitive material positioned within a shell. The shell has a first section and a second section, which are attached together by a non-adhesive bond. The non-adhesive bond is an atomic bond, such as a diffusion bond. The temperature sensitive material is capable of emitting a radiation signal which varies in its magnitude and character as the material""s temperature changes. The shell allows transmission of the radiation signal through the shell to an external processor. Analysis of the emitted radiation signal by the processor provides a temperature measurement of the temperature sensitive material.
In one embodiment, the temperature sensitive material is a phosphorescent, such as a phosphor. The shell may be made of a material that can be diffusion bonded, such as a sapphire or a quartz. In other embodiments a silicon comprising material, a glass, or a plastic is used for the shell. The diffusion bonding seals the shell, thus preventing the temperature sensitive material from being exposed to the surrounding environment. This reduces the potential for contamination of the adjacent structures, such as the substrate or chamber. The likelihood of contamination is also reduced since the diffusion bond lacks any adhesive, which could otherwise discharge into the surrounding environment. The temperature sensitive material can be protected from radiation heating by a reflective member.
The sensor can include a stem attached to the shell. The stem can function to secure an optical fiber in a position where it can transmit and receive radiation signals to and from the sensor. In some embodiments the stem contains one or more waveguides, which likewise allow the transmission and reception of radiation signals to and from the sensor. The stem may be a sapphire or a quartz, which is diffusion bonded to the shell.
In certain embodiments, the stem includes waveguides which allow the transmission of two or more separate radiation signals. One waveguide is used to transmit radiation signals to and from the sensor, which has a first temperature sensitive member, and a separate waveguide is used to transmit radiation signals to and from a second temperature sensitive member. In such cases the second temperature sensitive member can be used to obtain temperature measurements of adjacent structures, such as the substrate support. A prism can be used to direct the radiation signals between the second waveguide and the second temperature sensitive member.
In some embodiments of the present invention instead of a stem, a single waveguide is mounted to the shell of the sensor. An example of such an embodiment has the waveguide positioned to a side of the sensor in a cantilever arrangement. Such waveguides can use a prism to direct the radiation signals between the waveguide and the sensor.